An electromagnetic fuel injector comprises a cylindrical tubular body having a central feed channel which performs the function of a fuel duct and ends with an injection jet controlled by an injection valve operated by an electromagnetic actuator. The injection valve is provided with a plunger, which is rigidly connected to a mobile armature of the electromagnetic actuator in order to be displaced by the action of said electromagnetic actuator between a closed position and an open position of the injection jet against the action of a spring which tends to hold the plunger in the closed position. The plunger ends with a sealing head which, in the closed position, is thrust by the spring against a valve seat of the injection valve in order to prevent the fuel from escaping. In general, the sealing head is arranged within the fuel duct; consequently, in order to change over from the closed position to the open position of the injection valve, the sealing head is displaced in a direction contrary to the direction of feed of the fuel.
Electromagnetic fuel injectors of the above-described type are simple and economic to produce and exhibit a good cost/performance ratio. However, such injectors do not ensure a high level of precision and of stability in directing fuel injection and such injectors are accordingly unsuitable for use in “spray-guided” engines, in which the fuel must be injected with a very high level of precision in the vicinity of the spark plug; indeed, in this kind of application, an error of less than one millimeter in the direction of the stream of fuel may result in wetting of the spark plug electrodes, so seriously compromising combustion.
JP3050378 discloses an injector for directly injecting fuel into a cylinder of a two-cycle engine; the injector is provided with a two-piece structured valve member in a housing for guiding freely movably a first valve member provided with a valve head at the tip along the axis by a guide member and a sheet member. In this case, a cone-shaped fuel injection port expanding outward is formed at the tip of the sheet member; in addition, a fuel measuring unit for giving a constant flow path cross-sectional area corresponding to difference between the cross-sectional area of a fuel path and the cross-sectional area of the valve member in the flowing direction over specified length and regulating fuel injection amount per injection is formed before the injection port by providing a neck at the foot of the valve head.
JP62255569 discloses a fuel injection valve; first and second stoppers serving as stoppers on a moving side are made abutment against a spacer serving as a stopper on a fixed side for keeping an operating stroke of a needle valve constant. When an amount of fuel injection is to be regulated, a screw serving as a regulating unit is move upwardly and downwardly while fuel is injected for thereby determining the position of a valve case with respect to a body so as to regulate the operating stroke; at the time, the urging force of a regulating spring permits the valve case to move together with the screw and the spring permits the needle valve to move together with the valve case. When a position of the valve case corresponding to a prescribed injection amount is reached, the screw is fixed to the opening lower edge of a body by spot welding.
JP3043659 discloses an injector directly injecting a fuel into the cylinder of a two-cycle engine; the injector has a valve member divided into first and second valve members, and the first valve member is guided by a guide member and a sheet member and held in such a manner as to be axially movable, and a valve head is provided on its top end. The second valve member is projected into the solenoid of an electromagnetic driving means, and an armature is fixed to its rear end part. In this case, a return fuel passage extending from a bypass passage forming a part of an injection fuel passage extending from a fuel feed port to a fuel injection port provided on the sheet member inner end side to the fuel tank side is formed.